Temperature resistant composites made using multifunctional maleimides are well known. (Multifunctional maleimides, as the term is used herein, means compounds having at least about two crosslinkable maleimide groups per molecule.) See, for example, U.S. Pat. Nos. 4,654,007, 4,644,039 and 4,618,652.
Thermosetting resin compositions comprising multifunctional maleimides of the prior art are potentially very valuable because the temperature resistant thermosets which result from curing them also have advantageous mechanical and chemical properties, including hot/wet properties.
One characteristic of the aforementioned prior art thermosetting compositions, however, is the high density of crosslinks resulting from addition polymerization and other crosslinking of the multifunctional maleimide. These densely crosslinked thermosets are accordingly susceptible to thermocracking during the curing operations and subsequent heating and cooling cycles. Moreover, thermoset composites comprising high strength filaments and thermoset resin matrices made using multifunctional maleimides, have suspect damage tolerance due to the brittleness of the densely crosslinked resin matrix.
Recently, efforts have been made to reduce the drawbacks of thermoset composites made with multifunctional maleimides. For example, U.S. Pat. Nos. 4,518,754 and 4,518,755 suggest use of other unsaturated monomers in combination with the multifunctional maleimide. Also, copolymerization with certain alkenylphenols or dialkenylphenol ethers as reactive diluents has been proposed (see U.S. Pat. No. 4,100,140). And copolymerization with N-vinyl-pyrolidin-2-one and acrylamide (U.S. Pat. No. 4,413,107) has been disclosed. Other exemplary approaches have included modifying the multifunctional maleimide itself (e.g. U.S. patent application No. 761,432, of Aug. 2, 1985 now U.S. Pat. No. 4,654,407) and the use of unsaturated oligomers in combination with multifunctional maleimide e.g. U.S. Pat. No. 4,647,615.